The invention relates to a system for detecting particles carried by a fluid flow. Detection of particles in a fluid flowing through a conduit is often desirable, in particular when monitoring flows of well fluids such as water and/or oil and/or gas being produced from underground permeable formation layers that are penetrated by wells extending from the surface of the earth into the said layers.
The fluids passing out of the formation layers into the wells are transported through the wells to the surface. Often, these fluids carry solid particles such as sand grains that are dragged from the formation layers by the flowing fluid. These particles will damage the production equipment, such as by erosive action, or settle down in parts of the equipment, thereby necessitating frequent cleaning of the equipment. To prevent this, the fluid flow should be monitored in order to allow the operator to take the necessary steps when unallowable amounts of sand grains are found to be present in the fluid flow.
To monitor the fluid flow carrying particles therewith, use has been made of systems including a metal rod that is exposed to the flow of fluid. The particles on impinging against the rod, generate acoustic energy, which energy is detected by an acoustical transducer means (such as a piezo-electric element) cooperating with the rod. The transducer means generates electric signals that are representative of the acoustic energy generated by the particles that have contacted the rod. By gauging or calibrating the system, reference data can be obtained that are representative for the total amount and/or mass of particles that is present in the flow.
It has been found that although the measuring results obtainable by the above systems are reliable in single-phase flow, problems arise when applying the systems in multi-phase flow, such as in a two-phase flow, in particular when the two phases are a gas and a liquid.